Nonlinear transport theory in the metal with tunnel barrier

Within the framework of the scattering matrix formalism the nonlinear Kubo theory for electron transport in the metal with a tunnel barrier has been considered. A general expression for the mean electrical current was obtained. It significantly simplifies the calculation of nonlinear contributions to the conductivity of various hybrid structures. In the model of the tunnel Hamiltonian all linear and nonlinear contributions to a mean electrical current are evaluated. The linear approximation agrees with results of other theories. For effective barrier transmission $\tilde T = 1/3$ the ballistic transport is realized with a value of the Landauer conductivity equal to $G = \frac{{2e^2 }}{h}$.